Space telerobot systems may contain forty or more motors under computer control. Most robot motor control prior to the advent of this invention was done on a customized basis with each manufacturer using a different controller design which was tailor-made to the motors being used. The result is that, in the past, there has been no universality, and existing components designed for one system could not readily be adapted for use in some other system. In addition to universality, there are many applications which require versatility and modularity. Space operations as described herein are typical of such applications.
Future space operations relating to space station, satellite and space platform servicing, maintenance and assembly call for an increased application of telerobots. The term telerobot denotes a mobile and manipulative machine which can be controlled in both teleoperator (man-in-the-loop) and robot (automatic/autonomous) modes of control. A typical machine of this category is illustrated in FIG. 1 of an article by the inventors hereto entitled "Universal Computer Control System (UCCS) for Space Telerobots", IEEE Proceeding of The International Conference on Robotics, 1987. The typical machine of FIG. 1 of that article has redundant arms, multi d.o.f. end effectors, and several TV cameras and light sources on independent multi d.o.f. platforms. The mobility unit itself, to which the dual-arm system is attached, can be a multi d.o.f. arm. The number of actuators or motors required to drive the articulated elements of a typical telerobot machine of this category can be thirty or more. Teleoperator mode of control with telepresence implies feedback to the manual controller and requires that the articulated elements of the multi (six or more) d.o.f. manual master controller be backdriveable by motors For controlling a dual-arm telerobot system in force-reflecting manual mode of control, fourteen or more motors will be integrated with the master arms in the control section. Whether teleoperator or robot control is involved, both locations must have essentially real-time information of what has transpired at the other location. In a teleoperator mode, software such as a display readout/visual display is essential.
Robotic control mode, by necessity, implies computer control of the motor elements of the robot machine. Teleoperator mode of control with force-reflecting and other sensing based telepresence capabilities also implies computer control of the master arms and motors. Two systems are described in Control of Remote Manipulators, Handbook of Industrial Robotics, Wiley, New York, Chapter 17, pp. 320-333, 1985 and S. Lee, G. Bekey, and A. K. Bejczy, computer Control of Space-Borne Teleoperators with Sensory Feedback, Proceedings of the IEEE International Conference on Robotics and Automation, St. Louis, MO, March 25-28, 1985, pp. 205-214.
Computer control in the past has involved hybrid systems in which at least some of the motors, in either the control or sensing loops, includes analog signals. A search of prior art related to this invention was conducted. The patents resulting from the search include the following:
______________________________________ Inaba 4,475,160 Hutchins et al. 4,488,241 Niedermayr 4,611,296 Japan 60-230206 Japan 60-214007 Japan 57-113118 Eder 4,099,107 Lee 4,300,080 Iwata 4,621,331 Sugimoto et al. 4,621,332 Pollard et al. 4,362,978 Takahashi et al. 4,639,652 ______________________________________
Of these above-identified patents, only a few require additional mention. First, attention is directed to Inaba 4,475,160. This reference, in FIG 2, discloses a circuit for sensing an abnormal condition in a robot arm motor including sensing the motor drive current by means of current sensor CT. Circuit ADC converts the sensed current to a digital signal and then CMR compares this digital signal with preset limit values. See column 3, line 60 to column 4, line 34. Also, see column 5, lines 9-46.
Next attention is directed to Hutchins et.al. 4,488,241. This reference, in FIGS. 5-8, discloses a computer controlled robot arm system wherein a plurality of robot arms are controlled by a computer with control signals and feedback signals traversing a data bus. See FIGS. 5-8 and column 7, lines 43 to column 8, line 5. The Hutchins et.al. reference particularly emphasizes its ability to deal with abnormal conditions for robots (column 1, lines 56-65) and using motor drive current for sensing and control (column 2, lines 11-20). Hutchins et.al. also employs computer data for control with the capability of dynamically inserting correctional data in the robot instructional data (column 2, lines 21-27).
Next, attention is directed to Niedermayr 4,611,296 which discloses a robot arm control circuit including a plurality of tactile sensors providing feedback signals from the robot arm to a programmable sensor interface for generating kinematic control signals See FIG. 1 and column 4, line 58 to column 5, line 35.
Next, attention is directed to Japan 60-209802 which discloses a circuit for sampling the load current of a robot arm motor and processing the sampled data with a RAM to determine if the load current has exceeded a preset limit.
Next, attention is directed to Japan 57-113118 which discloses a robot control system which stops robot operation when the driving current exceeds a preset limit.
Japan 60-214007; Eder 4,099,107; and Lee 4,300,080 all disclose a closed loop servo system wherein motor current is sensed and fedback for control purposes.
A flexible computer control is eminently the most reasonable approach when the manual master controller is not a kinematic and dynamic duplica of the robot arm, but instead takes the form of a generalized force-reflecting hand controller which is interfaceable to any robot. Such a master controller is exemplified by an experimental device that has been developed at the Jet Propulsion Laboratory (JPL). In that experimental device, the kinematic and dynamic relations between master and robot arms are established through mathematical transformations embodied in computer programs in the control station. See A. K. Bejczy and J. K. Salisbury, Jr., Kinesthetic Coupling Between Operator and Remote Manipulator, Computers in Mechanical Engineering, Vol. 1, No. 1, July 1983, pp. 48-60.
The large number of computer controlled motors in space telerobot systems, and the inherent requirement of their computer control coordination, was the motivation behind the JPL research and development of a Universal Computer Control System ("UCCS") for all of the motor elements of a space telerobot system. A review of the above-noted patents and publications discloses that none of the relevant prior art discloses the hardware/software features of this UCCS invention including, in particular, all-digital signals throughout the UCCS.